Transoceanic cable circuit



1931- H.-W. DUDLEY TRANSOCEANIC CABLE CIRCUIT Filed Aug. 8; 1930 3 Sheets-Sheet 1 ll. E m fi INVENTOR H. WDUDLEV "J ATTOR w ut Nov. 3, 1931. H. w. DUDLEY TRANSOCEAILIC CABLE CIRCUIT Filed Aug. 8, 1950 3 Sheets-Sheet 2 INVENTOR H. W DUDLEY A TTORNE Y NOV. 3, 1931. w, DUDLEY 1,830,226

TRANSOCEANIC CABLE CIRCUIT I Filed Aug. 8, 1930 3 Sheets-Sheet 3 l VC I EEG IIJ

INVENTOR H M. DUDLEY ATTO NEV l You I present invention is particularly applicable i's disclosed'in' anapplicationof G. Crisson Il a tented Nov." 3, 1931 eonmwrsemez or nAsrr ORANGE, nnw annsnrj ASSIGNQR r0 BELL TELEPHONE 'rnnnsoc nhnrc onizi nv orn-co r This invention relates totransmission contime such as a tra'ns oceaniclcablev s systemjof the generaltype to which the and s. 'B. lVright "Serial 'No." 391,598; filed .Sept.:1o, 1929-.' Inthat systemacable station' is connected by land lines to 'a-distantly' locatedterminal station where provision is inadefor extendingjthe circuitso as to enable commercial? tel phone connections to be I made to ';the terminal' station andthence 'to' the-cable from any desired'poinnIeither directly' from a subscribers's'tation' or over 'a toll-line. The principal supervision ofthecircuit, including setting up of connections,

7 observation of the service and'c'ontrol of the s f. transmission, is exercised at the land line'ter- H min'al station,the-supervision and'attention. that is necessaryat'thecable station beingof afseco1'1daryforde'r, such as testingand'cir V cuit maintenance. Voice operated switching 1 7 devices are used at the cable station for enabling the cableto be connected alternatively I J to fatransmitting circuit" 'a'nd to a receiving circuit, *one at 'aftimei-QSince the cable .has high; attenuation, high {power amplifiers are necessary in -the transmitting circuitfandf high-gain low-level amplifiers are necessary in'the receiving 'oircuitif-iThe; main function I of the cable stationswitching circuits is to efl'e ct thi'salternative connection ofthe cable" to the transmitting or "tothe' receiving circuit as required and to" prevent circulation of en' ergy (or singingyin this cable terminal cir cu'it. involving asl it does, extremely highpam- I "plification. At the landline termin'aLsta- :tio'n,o n the other" hand, commercial speech] levelsaredealtfwith, so that 'the iapparatus at 'th is' station is joflessfspecial design; the

' principal function's here being to adapt the circuit to the dilierent'transmission requirements of the various-connections and 'tofexeri cise control over thes'v'vitching 'and other ap paratus at the --distant b-1e station. 5' There Y must, of course, be close coordination at all times between the 4 terminal station and the cable stations...

.One; object of thepresent invention is to improve the coordination between the terminalrand cable stations by giving the terminallstation m'orepositive control ofthe cable stationand by improving transmission control at and between said stations. I A'l feature 0f the invention comprises the a use oiacontinuous wave to control the various switching operations, in whole or in part,

feature, as a gain control wave.

' -A further feature comprises a switching circuit which-wgivesthe receiving echo sup monaron rrzs, 'rrriconronaran, or New Yon fn. 71;, conroRA'rIoN on NEW this waveservingalso according to a further,

A further feature comprises an improved receiver input connection from thecable.

I Further objects and features will appear more fully from the following detailed description of preferred'embodiments disclosed inthe attached drawings.

The present invention will be described in connection with a single-core cable with send-- ingand receiving sea earths, as disclosed and claimedin an application of A. M. Curtis, Serial No. 382,011, filed July 29, 1929. On

the assumptionof equal lengths andequal propagation constants, and the same values of input current, it can be demonstrated th'at while 3 db. more power is-required for a twin-corethan for a single core cable, the receiving signal voltage is 6 db; greater. The

resistance noise is of the same magnitude in a 'twin-core as in a single-core cable with a receiving sea earth in which the artificial line resistance balancesthe cable. The resist'anc'e' n0isefis 3 db. less if the receiving sea earth is omitted; As regards signal-tonoise 'ratio,' therefore, thetwin corej cable is" 3;db.jbetter than the single-core cable with: outfeceivingsea earth and is 6 db. better than 'a "single-core cable with receiving sea earth. This'leads to the result that a single core cable without receiving sea earth should be designed for-3 db. less attenuation than thel corresponding twin-core cable, and that a single' core cable 'withreceiving sea earth should be designed for 6 db. less attenuation stood from the. following detaileddescrip= side with Fig. 1 at the left sho'tv'theltwo" than the corresponding twin-core cable,'on the assumptlon stated above. The assumption ot the same nput current lnboth cases is made in View of the fact that the loading material (or other factors) places an upper limit on the permissible transmittingcurrent I level.-

l The invention I be more under tion taken in conjunction Withthe drawings 1n ;Wh1ch"F1g. l and Fig.- 2 whenplaced'slde ends of a .complete terminal. system includ- 'i'ng thecable station (Fig.2) andthe termi? nating or control station (Fig. 1)--;. Fig. shows an alternative type of gain control ciruit togthatshown imFig. 2.;yand FigL-Ataisa key schematic showingan alternative scheine oftransl'nission control to; that. oft-Figs. 1

53:31 lwrlfl. i 1:; Referring first to Figs. -1 and 2; therland line.

LL; with the usual hybrid coil 10, and: balance to theflistant. cable 1 station of Fig. 2. -Here i'tQincludes transmitting amplifiersiandpother apparatus 'toibedescribed later,' and tenni nates in alsuitableeconnectingcircuit for-the cableitsel'l uvvhich is indica'ed at CL.

-SimilarlyTthe"receivingvbranch-13 of F 1g.

l lisze zgten'ded theopposite sideot'the four- I lWlI'B icircuit leadingfrom thecable. station in,Fig. 2-,-iwhereiit includes su1table-1ampl1-I *fiers and other cableterminal apparatus and a QhliQQtsi :to; the f receiving. ,zcircuit of the y As stated-above,gvoice operated switching 5-; employed at both Athe land line terminal;

and thejcablewstatiom. the jla'tterv being auniliarytotheforiner The provision of.

directional-switching the land line .ter-

' minal doesnotniake. llliPOSSlblGtO eliminate; switching-e; at :the=1; cal )ler station. :The}. cable: station} mustfput in, sufficient loss to: prevent) singing-at all timesu yTheland li-neterrninal-adoes. -no,t {need to 7 put in excessive 1 loss .since' 'singingpannot joccuridue toits failure. land; line must discriminate be-.- tween speechlandnoise and? keepf clipping" downitoaminimum g The cable stationmust function in .phasewith the-landline terminal. unless blocked by received speech and should. be; designed to. give [no additional clippingr- Since; the land line} termin a-l. does not, have thgtmotion; of preventing singingit ispref-j erable he 7 switch ng isv onlthe transmitting side since, this; stationjisto; exercise the, .ln aincontroly {The prin i l apparatus gin-the .transmit- The ting branchof the land line terminal com' prises input amplifier 14, volume control cir disabl'er "is shown as comprising amplifierrectifier 19,.and associated relay 20." A'seo the land lineteri n'inal a device to disable the transmitting -speech'.path during receiving to prevent an unbalance or echo current, on receiving, from setting up jthefl transmitting circuit. '1; This ondrelay'21 is'also operated from the ampli-' fier-rectifier .to, remove loss from the receiver for afpurpose to .b edescr-ibed later. 7 V

':The .ainplifier-rectifiers: l-7 ,i-:l9, may be of any. appropriatetype ,afor. converting ,spe ech waves; vlnllOj'gdirect 1, currentfsuitable for con trolling f relaysr .iThe-i rvolume control: 165': is preterablyof the type shownain applicatiom Serial No. 375,629 filed July 3, 1929;byjl. li.

Hogg although; 1 any suitable type, 5 either manually, or automaticallyoperated may: be

used; -.-:The delay device 16 maybe azlow ip a ss .iilten type} ot-sectional. network or.- other elec:

tr cal type, ;0racoustical ormechanical yot which ,a,ll ,three types are lUlQWIl l'Il' the prior -q h, .engmianig been; 122.15 ,appears! in the cable station, 2, leads firstthrough a. gai n control circuit 30 to be later. 1

and then; through filter 31;, 'eq all-ZQI 32f amplifiers 33,,3t .and.35-,-;series' capacities 3 6 (wh h utd wn the. lo que es n present their being sent into the cahlelfj, 111 5} former 37,across which is connected a pro;

tection 'l e 8. such; a a.gas. l ed t1j bewith; suitable breakdown; voltage. and. finally the nor al y o en-c nt c siv tehing re ay 39 to:the cable'iitself The connection-of the transmitter leads to the qcable is made bemeetin ,tat-1eme andl ihe sending sea I -.receivingbranch 2 ing the cable; (between c or ,e andre J ceivingnsea earthincludes normally closed contact of switch n relays' 39 and shielded-L transformer series capacities.47, step-11p I V transformer. A 8, '-=16C61Y1I1g, amplifier 49,

equalizers. 50; 'sljfiner i satanic ampli ers asrshoi'vn. including in partieula'rv thesrvitch SO and 51 are" forithe purposej ofiequalizing for theiunequa'l 'at tenuation v by the. cable -"over "the I transmitted ,frequencv..ran, ;e. andeffectingjalnyfurther i p e i ik s ort o t at inerseesaw 1 desirable n .order to "obtain-as qualityf pe -2 11f ien imse a -flr eerfiie e re sible." ispreferable to havetheequalizers eiving' path. j The land line' termlnaly' eepest-fi nds f h l i-se'fiect we I ancomple nentaryi distortion j to. thatof the I LL (suitable and 84).

amplifiers are indicated-at V 83 I The purpose of the impedance network 81 isto provide, in efl'e'ct,a margin of sensitivity for the receiving disabler-circnit. v Itwill' be noted that volumecontrol is provided in the input of circuit 12 and ahead of the aim plifier-rectifier 17. This is desirable for several reasons, one of which is that it is desired to have amplifierfrectifier 17 o erateat'com stantfvolume; As different su scriberstalk over the circuits: and difi'erent lengthiconnem tions are-used, it is apparent that thespeech Volume received"over'thelline LL will vary considerablyfi The volume control 15, in effect, equalizes these variations Which means 7 that at'times amplifier-rectifier-17Will re;

spond to currents-ion line LLthat are Very inuch'weaker than at other times. a In eifect' 'tliereforeythe" sensitivity of the amplifierrectifier 17 is increased with respect to .the

raised at 15. c

o It is necessary that amplifier-rectifier.-19-

received speech on-line-LL as-tlie volume is "i ",bemade sufficiently sensitive to insure its'op- "eration by the weakest-received speech in circuit 13 that wouldbe capable vofoperating amplifier-rectifier 17 upon finding-its way across from circuit 13 into circuit v12 due to unbalance ofthe hybrid coil, or'fany other reason. ,Since it is desired to make amplifier-' rectifierl? of high sensitivity to avoid '6XC6S- sive delay and tofprevent clipping,this-places very high requirements on the disabler circuit 19 unless means are provided to give a sensitlvity margin to the latter.

i Thissensitivit'y margin is provided by network 81 and relay 21. lvhenever amplifien eration ofthe echo suppressor will be highly attenuated (for example, 10 db. at 81*before reaching the hybrid coil 10. Asregards their effect on amplifier-rectifier'17therefore,

I it is seen that a sensitivity margin exists" in rectifier 19 is in its normal or unoperated con- 'dition', network 81 is in its maximum loss con;-

dition since its shuntis closed. Therefore any-received waves whl'ch fa1l--to cause 0p-v favor of echo suppressor 19;

I The network 81 does notiintroduce addi tional-loss to the speech sinceit is;cut 'out' ofcircuit by relay 21 whenever speech is beingrec'eived. The order of operation of y the relays-is preferably such that relay 20 opens its back-contact before, or atleast as soon as relay" 21*'operates. The increased sensitivity obtained by use'lof network 81a nd v relay 21 permits the use of smaller trans; mitting time delay in delay" network -16 and smaller hang-over time for preven initial and'final clipping. :i;

Thereare several' advantages in using" a; tone frequency wavebetween the land" line terminal andfithe c able sta ion. The tone 4 frequency enables fasteroperationof the apparatus' controlled by it .atthe cable station circuit at the cable station. It is also pos- 'sible to secure a bettermargin over noise by using atone frequency wave than if speech Waves Were employed directly to control the transmitting possible without unduly increasing the power transmitted over the connecting line. For example, the control frequency may represent only 10% of thespeech power transmitted. The control frequency also gives the effect of a higher sensitivity for the transmitting amplifier-detector at the cable station without actually having a sensitivity as high, thus making for both quicker operation and less liability to false operation by noise. 'One reason for the effect of greater sensitivity is that the control Wave is sent out at a constant amplitude and the make amplifier-detector; This is and break at the'beginning andend' of the i wavetrains represents a sudden transition, Whereas in the case of speech, the initial sounds often-times represent slowly growing energy andthe final sounds trail off into gradually decreasing energy. These efiects are-not favorable to positive actuation of the switching circuits. In addition to the foregoing advantages of the tone frequency, there is the further advanatge of convenient regulation for va-' riations in the transmission equivalent of the interconnecting circuit as has already been described.

{An alternative circuit for "regulating the transmission is shown diagrammatically in Fig. 3. The circuits included Within the broken outline of Fig. 3 are intendedto replace those in the'outline labeled 2- 2 of Fig, 2, the terminals'labeled 85 in Fig. 3 cor responding to terminals, 85 of Fig. 2. using the alternative circuit of Fig. 3 the con-'- ductors 86 of Fig. 2 are broken at the iunc tion indicated bythe small circles in Fig. 2' and vacuum tubes 64 and 65 are therefore rendered without effect.

Referring in detail to the circuit of'Figj 3 the amplifier 7 5 and resistance pad 30 correspond to those of Fig. 2. The-tone frequency comingfrom the land line terminal over circuit 12 is selected. by band filteri 87 which partly or wholly, excludes speech and is .rectified in the amplifier-rectifier 88 to produce current flow; through resistance89. fVacuum tubes 64 and 65' and transformer 66" per-'. form similar functions to elements 64, 65 and 66 of Fig. 2. That is, these tubes acting through winding 66 supply a shunt ima pedance across circuit 12 which is varied under control-of conductor 67 leadingito resistance 89. As the amplitude of the received control wave varies, the shunt am. pedance produced by tubes 64 and 65' varies at the same time and in the proper direction and amount to maintain constant level'in the cycles persecondywithout the employment circuit-12 to -thei ight o ietivorkl ifiO in- Fig. 3.- T'One advantage of t arrangement over that ofiFig 2" is that constant level-is maintained for-thecontrolycircuit 85 leading to the transmitting amplifier-detector.

*Some further detailed description will now; be given of the receiving circuitat the cable'station. It Will be noted that the receiving I transformer 46 has its primary per manently' connected to the main circuit ground which is the sendingsea earth; This effectively prevents high voltages'from being developed along the receiving circuit Which might result gin af cli'cl'r.1 The secondary Winding shield 1s grounded at the I receivingamplifier ground. r

The series capaclties i"? together' vvith the inductances infthe. circuit provide the effect 7 V I ofa high'pass'filter-which greatly attenuates the veryjlovv frequencies (under about 100 of additional resistanceshich might in crease theresistance" noise. This netwv-ork'is capable ofproducingaloss; at 50 cycles of about 50 db 7 This high loss-at the verylow frequencies 1s important both from. the I standpointofincreas ng thed'ecay of relax-a tion current as Well as discrnninating against low frequency interference from neighboring cables or other sources. -,The .series ca-' pacity represented condensers 47 may be.

of the order of r 1 to 2 inf. and the "step up ratio ofinput coil 4-8 may beorgreater;v

Passing along to the receiving amplifierdetector vthis should have a hang-over time suficient to insure thattlie 'lastof the speech andtone'wave'energy haslhad' time to'reach the land "line terminal. and release relay 2O thereatand toallow for the dissipation of any energy inth'e interconnecting.line- (13)" .7 between the twostations'of Fig; landF-ig.

V 1 those -=of .the previously described} The arrows represent,switch-mg closing control is indicated by athird n r ch-rectedtoward the .po nted contactsi of the 2 after relayQO has been released; i In other Words, t1he hangover time should the about vtwiceithe timeof'transnns'sion between stationsof Fig-.;-1*and Fig-2; r i i Instead of using separate- -tone frequency sources-'fonthe cable and thein'terconnecting 1 line circuits,a single source oftone -frequency may be used for :each direction I of transni s- 31011 through the entire systenr The manner in Whichkt-his is a-ccomplished isillus -v tr a ted in Fig.4. i g r This figure is nasingle' line schematic in; which the circuit details maybe thesame as ii gures. I I points: When two of thepointsare"shown incontact inthe figure this ,means-- that the circu is normally established at thatp'oint. [The $1-- gle arrowhead indicates that some sort of control is effectedlat .thatfpointf lfVhenatlre' arrows are separated, 'CllIS -HLQQIDSlllEIlL-jtllfi circuit is normally ripen, The openingand which 7 NewYor Newfo two arrows The; actual form which the switching contacts may take is illustrated and described in connection with the previous figuresandmay comprise a relayor Circuits fo'r disabling an amplifi r or the like. lIflhe land line is indicated at the leftofihe figure and the cablecircuits for sending-and receiving are'respec'tively' indicated by 101 V therefore transmitted into the cable ovjeigthe sending lead" at 101. :The-tone freq'uei'icy also operates through the amplifier-rectifier 188 to control the regulator. circuit to maintain the level going into thecahle 0on stant aslregards variation in the attenuation of circuii 112.

The effect of the Wavesniinal-inay. be seen from considering theef fect of the received avesjnthe station of Fig. at. 'The received speech and tone frequency waves arrive over the cable .101 and pass through the normally, closed Contact into the receiving circuit 113. Thetoneffrequency' Waves actuate amplifier-rectifier: 171

an'ipliffier-rectifier 156-fat point 172., The speech and-control aves cont nue; over Where the tone frequency operatesamplifiere atthe distant tervrlcuit 113150 the distant land line terniinal Era isables Y the i circuit 20f transmitting rectifier- 119 which disables the transmitting vamplifier -rectilier at 120 and controls the loss network 18lat point 121. Band filter 1 82 corresponds to filter82 of Fig. 1. I The control frequency may be the same or different inthe opposite directionsof trans-,

'mission Assuming the speech rangegtobe from 275 cyclesupWard to some suitable upper limit, a control frequency of 200 cycles may be used forboth directions. The controlfrequency may be .used over 'onlyfa part I terminal and the cable terminal. 3 v

of the circuit, for instance between the land In: transatlantic, telephone cable,- the equipment at the left of 'thez broken', lines in tin Fig. 1;) may be located at as v v undland with similar equipment Ireland. That is, interconnectinglines12, 13,-or1l2 and'113-eXtend on theone side, from New York-to Newfoundiand, and onthe; ether lines (or that in Fig; 2') would be loca I hsim'ilar equipment at London while the equ pment at the right-ofthebro side, from London to Ireland, the, cable entending from fNew foiindland to Ireland;

7 tantlylocated control'f station, atransmitting amplifier at said transmitting station normally d sassociated from said l ne, asource of -continuous Waves atsai'd control station,

means controlled by signalsto be transmitted from said control station for causing continuous waves from said source to be transmitted to said transmitting station along with said signal, andmeans at said transmitting sta tion responsive :to the received continuous waves for operativ'ely associating said transnitting amplifier with said line to repeatsaid "signals into said line.

- .fantly locatedcontrol station, a transmit- 2. In a signaling system including a line, a transmitting station for said line, a disting amplifier, at saidtransmitting station normallyv disassociated from said line, a"

source of continuous aves at said control stat1on-, means operatedby signals to be transmitted from said control station for sending wavesfrom said source to said transmitting stationsimultaneously with said signals, and

fmeans at the latterstation operated by said contlnuous waves for operatively associating said transmitting amplifier with said line for enablingthesignals tobesent into said line.

i 3,.In a signaling, system a line,'a transmitting station for said line, a distantly lo-,

cated control station, a' circuit interconnecting said stat-ions,atransmitting amplifier at said transmittingstation, an amplifier and a source of continuous waves: at said control 'statiombothof saidamplifiers and said source of continuous Waves being, normally inopera- 1 tive to transmit, means'controlled by signals to be transmitted for effectively connecting I both the amplifier at the control station and waves from said source for effectively con-' said source of Waves to said circuit, andmeans' at the transmitting station controlled by I lgnecting the amplifier thereat to said line.

a. An input system for an ocean cable com- I prising a cable station and acontrolstation line'under control ofsignals to be transmit-.

tedfan'd' means at the cable station operated "by said-waves for effectively connecting said variations in the In a four-Wire telephone ci'rcuit'com prising a transmitting circuit and a receiving 5 circu t, 'a voice operated circu t associated withthe transn'ntting c1rcu1t,an echo sup-w P is ampl fier to the cable v andcompensating for transmiss on equivalent of pressor associated With the receiving circuit and controlhng sald voice-operated circuit,

, a loss element'normally in said receiving circuit following said echo-suppressor, and meanscontrolled by speech energy in the re,- ce ving circuit for removingsaid loss element om ec r uit.

a te e e ci c h g e ho: suppressor'therein, means for effect vely ncreajslngfthef margin of sensltivlty of said echo=suppressor with respect to other appa ratus associated with the system, comprising a loss elementnormally'connected in the circuit following the echo-suppressor, and means controlled received speechfor removing sa d loss element.

i The ,comb'nation with a signal-operated transmission control circuit, a transmitter made. operativeor inoperative by said circiiitfanda gain adjustment circuit also'operated from saidtransinission control circuit, and controlling the gain of's'aid transmitter. 1' '81. In a signaling system including a line, aftran's'niitting station for said line, a distant ly located' control station, a transmitting amplifier at said transmitting stationfnorma-lly disass'ociat'ed' from said line, a. source of con tinuous waves at saidcontrol station, means controlled by signals to betransmitted from said control" station'for sending to said transmiaingsmtio in [advance of said signa ls,continuousvvaves from said source, and means at said transmitting station responsive to the received continuous-Waves, for operatively associating said transmitting ampli fier withsaid'line to repeat said signals into sa d V a v a, c i

{ 9, In {a longfdistan'ce telephone system, a

transmitting, stationfan. amplifier thereat adapted for connection to and disconnection from the transmission path outgoing fromv said station, ,a :distant control station, having means, for sending to said transmitting station speech and energyzother than speech coincidentallyv with and for the duration-oi 'said 'speech, and meansia'tj the transmitting Q1 5. A system asdefined in claim 9,;inwhich ineansjare also provided at said transmitting station for adjusting the level of the outgoing speech under control of said, energy received from"the distant control ,stat'ifon. '7 1 Iii'a four-Wiretelcphone system, :00111- ing oppositely directed oneway trans inissionpaths, a voice-operated circuit con} t'rolliiigone patina disabler circuit therefor controlled by speech energy incident upon the other path, and means for providing margin of sensitivity'for'said' disablerfcom prising a loss clement normally inserted in said oth e Jpath following said disabler, and 

